Straight tubes are better in an engineering sense - all those curved tubes made engineers flinch, that is not the way to get strength out of steel tubing.
But it worked, obviously....
If the day of the manx hadn't largely been over by the time they appeared, the Tickle frames appear to be a better idea all around.
But are decidedly thin on the ground these days ?

There were about 20 versions of the featherbed all up, if you have any insights into what defines a replica by sight we'd be interested to hear.
We've had this discussion before ?
The factory bikes had a distinctly 'squarer' look to the main engine tubular housing than the road bikes...

I'm pretty sure that the drawing I had a look at, for production featherbeds, had identical geometry for Manxes and road bikes. The geometry of the frame comparing year by year, was identical as far as I remember, apart from material and wall thickness, and a couple of brackets. Anyone familiar with the use of "variant" drawings would be at home with the concept. The basic geometry was shown on one sheet, with an applicability list, odds and sods brackets shown on another sheet with another applicability list and so on. Glad to be proven wrong though!
There were many, many different issue states of the basic featherbed frame all of which were applicable to a particular year or model. Different bikes were built to a Specification, which was pretty much the overall controlling document. The Spec detailed everything required to make and assemble any given bike. A fairly sensible early version of configuration control really, before the Configuration Control experts moved in.
cheers
wakeup

My own featherbed frame was a replica, my friend's triton has a genuine manx frame. The radius of the top bend above the gearbox is not constant, it varies and is difficult to get right. The other thing is that if the featherbed gets subjected to too much vibration it can crack where the top of the pivot mounting plates meet the top tubes. Also at the top of the front engine mounts. The Tickle frame is a good design, and it would be easier to replicate from a side on photo, than a featherbed. What is the head angle and fork yoke offset of the standard manx frame ? The genuine 1962 500 that I rode still had 19 inch wheels, and felt beautiful, really confidence inspiring. If you got offline with it, you simply gave it more stick. I fitted 18 inch wheels to my featherbed replica, and from then on it always ran wide in corners - heavy and exhausting to ride. I never measured the geometry on those old frames, and they seemed to have very little yoke offset - I've always wondered about that. Another friend has 350 manx, I might measure it next time I visit him. I wonder how the Domiracer handled ?
I don't know anything about slimline featherbed frames and really don't care about them.

Alledgedly SEELY had bought the Manx tooling of AMC as well as the G 45 , and passed the Manx stuff on to Tickle . So in a sense - theyre genuine ( Tickle ) Manxes . All you could get then anyway New .

Domiracerish in the rear tubes , the Domiracer cant have handled like a complete pice of s... , as it did a 100 mph I.o.M. lap or two as a 500 , and got a bit of a workout as a 750 .http://www.youtube.com/watch?v=QjAYnDLaplY theres a replicar here . Riders in the WHITE leathers , so you can pick him .

While the manx is quoted as having the same steering head angle as the road bikes, manxes are shorter wheel base, sat lower, and had shorter travel suspension.
So is that 'same geometry' ??

Featherbeds vary considerably over the years - and the number of manx bits that are interchangeable with the road bikes are rather limited.
Some of the gears in the gearbox, the steering bearings and the air in the tyres ?
Everything else is different....

If you talk to Norvin builders, a Vinnie lump will slot into some featherbeds and not others.
So there are some significant differences, somewhere.
Ken McIntosh in NZ has pics on his website of all the different year manx type frames he can supply.
Interesting comparing the differences, although obviously they are only pics.

wakeup said:

I'm pretty sure that the drawing I had a look at, for production featherbeds, had identical geometry for Manxes and road bikes. The geometry of the frame comparing year by year, was identical as far as I remember, apart from material and wall thickness, and a couple of brackets. Anyone familiar with the use of "variant" drawings would be at home with the concept. The basic geometry was shown on one sheet, with an applicability list, odds and sods brackets shown on another sheet with another applicability list and so on. Glad to be proven wrong though!
There were many, many different issue states of the basic featherbed frame all of which were applicable to a particular year or model. Different bikes were built to a Specification, which was pretty much the overall controlling document. The Spec detailed everything required to make and assemble any given bike. A fairly sensible early version of configuration control really, before the Configuration Control experts moved in.
cheers
wakeup

I had a fossick around in the drawing stores in mid 1970. I'm not suggesting that there were no changes to featherbeds over the years because there were many. What I am suggesting is that the basic geometry of the frames when made at a similar time was as far as I could see was identical. At that time I can remember being vaguely surprised, so I went to have a look at the Specifications for a Manx and a Domi of the same year (late 50s if I am remembering correctly) and the basic drawing number was the same, obviously the material wall thickness etc. etc. was different. Because of the differences, obviously the part numbers of the completed frames was different, but the majority of the parts (leaving materials etc aside) that went into the frame assembly were the same.
By basic geometry I mean the steering head angle to some datum, radii of the bends, position of the swinging arm pivot, position of bends, things like that which are important on a drawing.
At the time NV employed a young lady Tracer to trace all the drawings in the drawing store, so that they could be micro-fiched ....the high technology of the day. I've often wondered what happened to all that stuff. Some of the drawings went back to 1907!! I saw a GA of a o.h.c. (CS1??) from about 1930ish, drawn something like 1/4 scale, ink on linen, complete with silver tank with black and red stripes, just beautiful. But then I was a draughtsman!! We had to use crappy paper drawing sheets with crappier plastic leads.... awful things.
cheers
wakeup

You are talking about a fairly rare bird here ?
Folks who have sat on it or ridden it may be rather thin on the ground.

BenG here has Heinz Keglers old Daytona Dommie, and posted a fair bit about it here.
He also has a facebook page with lots on it.
It was of course a slimline - Doug Hele at the race shop helm at the time, and the Daytona rules stipulated a roadbike frame (stop those manxes sneaking in ?).
It had a lot of manx parts in it though, just not the frame.

Paul Dunstalls organisation took over the contents of Nortons race shop, with possibly a few other participants along the way.
The Dunstall Dominators were raced quite extensively through the 1960s, and a fair bit of them can be found online if you search enough.
A fair mix of 500cc, 650SS and a sprinkling of Atlases.
Wiki says twin engines were placed in manx frames, but that is certainly not true for all of them ?http://en.wikipedia.org/wiki/Norton_Dunstallhttp://en.wikipedia.org/wiki/File:Norton_Dunstall.jpg

Very little printed material goes into describing the actual minutae of the steering geometry, you'd be lucky to find that anywhere.
Better to find bikes in museums or sheds, and have a look and see if it looks faintly original.
Dunstalls did a LOT of stuff for cafe bikes too over the decades, so there will be a fair bit of that mixed in too..
Inc for Commandos...

The Norton race shop bikes were sold to Dunstall and one other person to my knowledge.
The 500 Domiracer that Norton built in 1961 for the TT, later acquired by Paul Dunstall was fitted to the Lowboy frame, that is the top tubes were about one & half inch lower than the standard f/beds.

Looking at the Jamie Waters site (that guy just has too many motorbikes!!) there is a picture of what is supposed to be a "lowboy" frame. Whilst its obviously related to a featherbed, it seems a bit of a stretch to call it a modified featherbed. More like a developed featherbed, or Son of Featherbed, or 2nd generation featherbed. Not dissimilar to the Tickle T5 frame if you think about it, although there are differences. I wonder if Tickle had a good butchers at a Lowboy when he was developing his T5?
cheers
wakeup

We might mention again that Nortons had had an earlier version of a 'Lowboy' frame - for the manx.
This included a cut-down version of front fork yokes - with no top yoke, at all.
This let the rider really get down on the tank, with an unobstructed view forward.
Was uncomfortable though, and apparently not continued with.
Anyone got a pic/link, one of the classic mags showed one some years back.

Norton did various configurations of the f/bed frame. The lowboy Dominracer frame was built in 1961 for the smaller 500 twin to lower the top of the bike, Helne stated in the Norton book by Roy Bacon on the Domiracer section that the 500 twin engine was ideal for this, also that Helne wanted to use lighter weight tube , the Domiracer was lighter than a Manx, not so the Manx which was a rather tall engine, nevertheless as Rohan states they kept trying with new ideas for the Manx.

I'd still be interested in what the specification steering geometry was for the works 1962 500cc Manx , - rake - yoke offset, trail, wheel size ? I don't believe I will ever find an unmodified bike to measure.

I have a friend who owns two unmodified Manxes, a 59 and a 61, I should measure them.
I thought the steering head angle for the Manx was 27 degrees, so that is what I made my project bike at. The 27 degree figure was given to me by Terry Prince, who built the first 30 or so Egli Vincent frames for Fritz Egli. Terry said that when he and Egli were planning the design of the first frame, they decided to go with a head angle of 27 as this was a proven ideal angle, the same as one of the best handling bikes ever built, the Featherbed Manx.

Doug Hele and Co did of course do some works specials in the early 1960s, like the Daytona bikes and 650 domiracers,
that used slimline frames.
Paul Dunstall ended up with these, be interesting to see what he knows/knew about them...